Worldwide Lightning

This image shows the global average annual occurrence of lightning at a resolution of ½° by ½°. (Very large 300 dpi version – 1440k) The data was obtained from the following two space-based sensors:

The Lightning Imaging Sensor (LIS), is used to detect the distribution and variability of total lightning (cloud-to-cloud, intracloud, and cloud-to-ground lightning) that occurs in the tropical regions of the globe. The LIS is a science instrument aboard the TRMM Observatory, which was launched on November 28, 1997 from the Tanegashima Space Center in Japan.

The Optical Transient Detector (OTD) is a solid-state optical sensor similar in some ways to a TV camera. It is uniquely designed for the job of observing and measuring lightning from space.

Global Lightning Activity

Where does lightning flash most frequently? According to satellite observations, it occurs more often over land than over the oceans. And lightning seems to happen more often closer to the equator.

The map above shows the average yearly counts of lightning flashes per square kilometer from 1995 to 2013. Areas with the fewest number of flashes each year are gray and purple; areas with the largest number of lightning flashes—as many as 150 per year per square kilometer—are bright pink.

The map is based on data collected from 1998–2013 by the Lightning Imaging Sensor (LIS) on NASA’s Tropical Rainfall Measuring Mission satellite, and from 1995–2000 by the Optical Transient Detector (OTD) on the OrbView-1/Microlab satellite. Flashes above 38 degrees North were observed by OTD only, as the satellite flew to higher latitudes.

The higher frequency of lighting over land makes sense because solid earth absorbs sunlight and heats up faster than water; this means there is stronger convection and greater atmospheric instability, leading to the formation of thunder and lightning producing storms.

According to NASA’s Daniel Cecil, a member of the Global Hydrology and Climate Center’s lightning team, the data also have revealed some interesting regional trends. For example, scientists have observed a large number of flashes during the month of May in the Brahmaputra Valley of far eastern India. The heating and weather patterns are unstable and changeable at that time—just before the onset of the monsoon, which brings plenty of rain but much less lightning. In contrast, locations in Central Africa and Northwestern South America have large amounts of lightning throughout the entire year.

As the map shows, the highest amounts of lightning flashes occur in the far eastern Democratic Republic of Congo, and Lake Maracaibo in northwestern Venezuela.

Cecil noted that more years of data has not necessarily brought notable big-picture differences when compared to the earlier maps. “The longer record allows us to more confidently identify some of these finer details,” he said. “We can examine seasonality, and variability through the day and year-to-year.”

Where Lightning Strikes

Lightning. It avoids the ocean, but likes Florida. It’s attracted to the Himalayas and even more so to central Africa. And lightning almost never strikes the north or south poles.

These are just a few of the things NASA scientists have learned using satellites to monitor worldwide lightning.

“For the first time, we’ve been able to map the global distribution of lightning, noting its variation as a function of latitude, longitude and time of year,” says Hugh Christian, project leader for the National Space Science and Technology Center’s (NSSTC’s) lightning team at NASA’s Marshall Space Flight Center.

This new perspective on lightning is possible thanks to two satellite-based detectors: the Optical Transient Detector (OTD) and the Lightning Imaging Sensor (LIS). “The OTD and the LIS are two optical sensors that we’ve flown in lower Earth orbit,” says Christian, whose team developed the sensors. “The OTD was launched in 1995 and we got five good years out of it. The LIS was launched on the Tropical Rainfall Measuring Mission satellite in 1997 and it’s still going strong.”

“Basically, these optical sensors use high-speed cameras to look for changes in the tops of clouds, changes your eyes can’t see,” he explains. By analyzing a narrow wavelength band around 777 nanometers—which is in the near-infrared region of the spectrum—they can spot brief lightning flashes even under daytime conditions.